High Coercivity Magnetic Film for Use as Hot Seed in a Magnetic Write Head and Method to Grow it

ABSTRACT

A sub-structure, suitable for use as a hot seed on which to form a perpendicular magnetic main write pole, is described. It is made up of a buffer layer of atomic layer deposited alumina on which there are one or more seed layers having a body-centered cubic (bcc) crystal structure. Finally, a magnetic film made of FeCo or FeNi with an as deposited coercivity of 60-110 Oe lies on the seed layer(s). Coercivity is lowered somewhat after the annealing step. It is critical that the high coercivity magnetic film be deposited at a very low deposition rate of around 1 Angstrom per second. The magnetic film is preferably annealed at 220° C. for 2 hours in a 250 Oe applied magnetic field.

This is a Divisional application of U.S. patent application Ser. No.13/651,437, filed on Oct. 14, 2012, which is herein incorporated byreference in its entirety, and assigned to a common assignee.

TECHNICAL FIELD

The disclosed material relates to the general field of perpendicularmagnetic write poles with particular reference to the design andformation of hot seed layers on which such poles are grown (main pole isunder hot seed layers).

BACKGROUND

To further increase the storage areal density of the hard disk drive(HDD) system, there has been a growing demand for improving theperformance of magnetic recording heads. In a current perpendicularmagnetic recording (PMR) head, a single pole writer with a tunnelingmagnetoresistive (TMR) reader provides a high writing field and a largeread-back signal to achieve a higher areal density.

The single pole writer consists of a main pole (MP) surrounded bymagnetic shield materials from which the MP is separated by anonmagnetic spacer layer. The MP has a tapered shape whose tip faces themagnetic media as well as serving as an air bearing surface (ABS). Inaddition to the MP and the magnetic shield materials, a single polewriter also includes a pair of pancake-like conductive coils. These twocoils are connected through a center tab, with one placed above the MPand the other under the MP perpendicular to the ABS direction. Duringwriting, an electric current is applied through the coils, causing alarge magnetic field to be generated from the MP tip. This field is usedto change the polarity of the magnetic media.

A MP ABS view of a prior art design is shown in FIG. 1. In ABS view, theMP body 13 has a triangular or trapezoidal shape. As seen, the MP width(PW) defines the track width in the media. Soft magnetic shieldmaterials 15 are used around the MP with a nonmagnetic spacer inbetween. The nonmagnetic spacer 14 on the two sides of the MP is calledthe Side Gap (SG) and the nonmagnetic spacer 12 above the MP is calledthe Write Gap (WG). Above the WG, a high magnetic magnetization material11, such as Fe_((1-x))Co_((x)) (x=20-55 at %), Fe_((1-y))Ni_((y))(y=5-55 at %), or the like is deposited above the MP write gap 12. Thishigh magnetic magnetization layer 11 is the so-called “hot seed”.

SUMMARY

It has been an object of at least one embodiment of the presentdisclosure to provide a hot seed layer that is well suited to serve as asubstrate on which to build a perpendicular magnetic write pole whereinthe main pole is under hot seed layers.

Another object of at least one embodiment of the present disclosure hasbeen that said hot seed have high coercivity and low anisotropy.

Still another object of at least one embodiment of the presentdisclosure has been that said high coercivity be stable to temperaturesof up to 120° C.

A further object of at least one embodiment of the present disclosurehas been to provide a process for manufacturing said hot seed layer.

These objects have been achieved by first depositing one or more seedlayers having a body-centered cubic (bcc) crystal structure on the writegap. This is followed by the deposition of a buffer layer of alumina onthe seed layer(s). It is important for this buffer layer to be laid downthrough atomic layer deposition (ALD) so as to achieve maximum conformalcoverage.

Finally, a high coercivity magnetic film is deposited onto the layer ofALD alumina. It is a key feature of the disclosed method and structurethat this high coercivity magnetic film be deposited at a very lowdeposition rate (around 1 Angstrom per second).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an ABS view of a main pole of the prior art.

FIG. 2 is an ABS view of main pole with a FeCo hot seed layer that wasdeposited using a high deposition power.

FIG. 3 is an ABS view of a main pole with a FeCo hot seed layer that wasdeposited using low deposition power.

FIG. 4 a is an ABS view of a main pole with an ALD Al₂O₃ buffer layerand an overlying FeCo hot seed layer that was deposited using lowdeposition power, and FIG. 4 b is an embodiment of the presentdisclosure wherein the write gap is a composite with two layers.

FIG. 5 shows hysteresis loops of as-deposited and post-annealed FeCofilms using 2 KW deposition power.

FIG. 6 shows hysteresis loops of as-deposited and post-annealed FeCofilms using 0.5 KW deposition power.

FIG. 7 shows a plot of coercivity vs. deposition power for as-depositedand post-anneal FeCo films.

FIG. 8 is an ABS view of a main pole with bcc seed layers locatedbetween the hot seed layer and the ALD Al₂O₃ buffer layer.

FIG. 9 shows hysteresis loops of a 1,000 Å FeCo film grown on a Ta 50 Åseed layer in as-deposited and post-annealed state.

DETAILED DESCRIPTION

The disclosed material includes a method to grow a high coercivityFe_(1-x)Co_(x) (x=20-55 atomic %) film or a high coercivityFe_(1-y)Ni_(y) (y=5-55 atomic %) film as the hot seed layer for amagnetic recording writer. This method involves using a low depositionpower scheme in a Physical Vapor Deposition (PVD) system. When thisdeposition scheme is used, the coercivity of the Fe_(1-x)Co_(x) (xranging from 20 to 55 atomic %) hot seed layer, hereinafter referred toas the “special hot seed”, is greatly improved for both its as-depositedstate as well as for its post magnetic anneal state.

A buffer layer may be inserted beneath the special hot seed. This bufferlayer is an Al₂O₃ film, which should be formed by Atomic LayerDeposition (ALD). Additionally, one or more seed layers that have bcccrystalline structures may be inserted between the special hot seed andthe ALD Al₂O₃ buffer layer.

The special hot seed was processed in a Nexus PVDi system that ismanufactured by Veeco. The film is deposited at an Ar flow rate of 50standard cubic centimeters per minute (sccm), a process pressure of 3mtorr, and with a target-substrate distance of about 65 mm. The typicalspecial hot seed thickness ranged from about 200 Å to 1,000 Å.

The special hot seed film was deposited directly onto the WG. The WGmaterials are nonmagnetic and act as an isolating spacer between the MPand the hot seed. The typical thickness for the WG is 50-350 Å. TypicalWG materials are Al₂O₃, SiO₂, Ru, etc. The magnetic properties weredetermined by measuring hysteresis loops using a BH looper (SHBinstrument, Inc.) for the as-deposited films and annealed films.

Annealing is performed at a temperature between 180° C. and 300° C. andwith an externally applied magnetic field ranging from 200 to 1000 Oefor at least 1.5 hours, and preferably, at 220° C. for 2 hours in a 250Oe applied magnetic field. The deposition power, which in turndetermined the deposition rate, was adjustable. FIG. 2 illustrates a MPABS view for the case in which the special hot seed 21 was deposited ata relatively high deposition rate such as >3.6 Å per second.

In the first embodiment, as shown in FIG. 3, special hot seed 31, about500 Å thick, was deposited at a relatively low deposition rate such as≦3.6 Å per second. Typically, the coercivity of the special hot seedformed at the lower deposition rate was found to be greater than thatformed at the higher deposition rate. Thus, the lower the depositionrate, the higher the coercivity of the deposited film. In one example,the magnetic film has coercivity greater than 60 Oe, as deposited, andcoercivity greater than 30 Oe after being magnetically annealed.

In the second embodiment, as shown in FIG. 4 a, buffer layer 41 wasadded below special hot seed layer 31. This buffer layer was 50-350Angstroms of Al₂O₃ formed in an Atomic Layer Deposition (ALD) system.The ALD-formed buffer layer can serve as part of the WG 12 thickness asdepicted in FIG. 4 b where the alumina buffer layer 41 is formed on alower write gap layer 12 a. The ALD-formed Al₂O₃ buffer layer isamorphous, and therefore it has less crystalline effect on the hot seedlayer above.

The hysteresis loops of special hot seeds grown at 4.8 Å per seconddeposition rate (2 KW deposition power) are shown in FIG. 5. Anapproximately 300 Å thick Al₂O₃ layer, formed through ALD, was used asthe buffer layer. It was found that the as-deposited films aremagnetically isotropic with coercivity about 20-30 Oe. The overallcoercivity did not vary significantly post magnetic anneal but didbecome slightly lower in the annealing field direction.

The hysteresis loops for a special hot seed film formed with 0.5 KWdeposition power (1.2 Å/sec.) are shown in FIG. 6. An approximately 300Å thick Al₂O₃ buffer layer formed through ALD was used as the bufferlayer. These films were also magnetically isotropic but their coercivitywas greatly enhanced to about 100 Oe for as-deposited films. Thiscoercivity dropped to about 60 Oe post magnetic annealing but was still2.5 times larger than that of an annealed film formed at 2 KW depositionpower (4.8 Å/sec.).

FIG. 7 summarizes the coercivity vs. deposition power relationship forspecial hot seed films. The deposition power ranged from 0.2 KW to 2 KW,corresponding to a deposition rate range from −0.48 to −4.8 Å/sec. Allfilms had thicknesses of about 1,000 Å and were deposited on an ALDAl₂O₃ buffer layer about 300 Å thick. BH loop measurements showed thefilms to be isotropic. The coercivity increased nearly monotonicallywith decreasing deposition rate. The maximum coercivity (about 115 Oefor an as-deposited film and about 77 Oe for a post anneal film) wasfound to occur at a deposition power of 0.3 KW (0.72 Å/sec.).

FIG. 8 illustrates an embodiment wherein one or more seed layers 81 ofBody-Centered Cubic (bcc) material were inserted between the special hotseed 31 and WG 12 (including the ALD Al₂O₃ buffer layer). The bcc seedlayers serve to improve the bcc crystalline growth of the special hotseed layer, resulting in a higher coercivity because of the higherintrinsic crystalline anisotropy. For example, a magnetic film may beformed with coercivity greater than 70 Oe, as deposited, and coercivitygreater than 60 Oe after being magnetically annealed.

Additionally, since these bcc seed layer(s) are nonmagnetic, they can becounted as part of the WG thickness surrounding the magnetic recordingwriter's main pole. Materials for the bcc seed layer(s) can be Ta, W,TaW, Ti, V, Cr, Mn, Ni_(1-v)Cr_(v) (v=28-100 atomic %), Cr_(1-z)Ti_(z)(z=0-37 atomic %), including any combinations that crystallize assuperlattices.

FIG. 9 shows an example of this bcc seed layer effect. A 50 Å thick Talayer was inserted between a special hot seed deposited at low-power andthe ALD Al₂O₃ buffer layer. The as-deposited film was magneticallyisotropic with a coercivity of about 95 Oe. The post annealed film showsa coercivity of about 85 Oe. This reduced drop in coercivity confirmedthe advantages of the bcc seed layer insertion.

We claim:
 1. A process to form a magnetic film with a coercivity of sufficient magnitude for use as a hot seed in a magnetic recording writer having a write gap (WG), comprising: (a) depositing the magnetic film on a substrate with a physical vapor deposition process at a deposition rate in a range of from 0.48 to 3.6 Angstroms per second; and (b) annealing the magnetic film at a temperature from about 180° C. to 300° C. in an externally applied magnetic field ranging from 200 to 1000 Oe for at least 1.5 hours.
 2. The process of claim 1 wherein the magnetic film is selected from the group consisting of Fe_(1-x)Co_(x) wherein x is about 20-55 atomic %, and Fe_(1-y)Ni_(y) wherein y is about 5-55 atomic %.
 3. The process of claim 2 further comprising: forming a buffer layer of Al₂O₃ between 50 and 350 Å thick on the substrate with an atomic layer deposition process before depositing the magnetic film.
 4. The process of claim 3 further comprising: depositing one or more seed layers of nonmagnetic materials having a body-centered cubic (bcc) crystal structure on the Al₂0₃ buffer layer prior to depositing the magnetic film.
 5. The process of claim 4 wherein one or more of the seed layers is selected from a group consisting of Ta, W, TaW, Ti, V, Cr, Mn, Ni_(1-v)Cr_(v) wherein v is from about 28-100 atomic %, and Cr_(1-z)Ti_(z) wherein z is from 0 to about 37 atomic %.
 6. The process of claim 4 wherein the substrate is the write gap.
 7. The process of claim 6 wherein the Al₂0₃ buffer layer is also part of the write gap.
 8. The process of claim 6 wherein the bcc seed layer(s) constitute part of the write gap.
 9. The process of claim 2 wherein the magnetic film has a coercivity greater than 60 Oe, as deposited, and a coercivity greater than 30 Oe, after being magnetically annealed.
 10. The process of claim 4 wherein the magnetic film has a coercivity greater than 70 Oe, as deposited, and a coercivity greater than 60 Oe after being magnetically annealed. 